Electrosurgical forceps utilize both mechanical clamping action and electrical energy to effect hemostasis by heating the tissue and blood vessels to coagulate, cauterize and/or seal the tissue. As an alternative to open forceps for use with open surgical procedures, many modern surgeons use endoscopes, laparoscopes, and endoscopic/laparoscopic instruments for remotely accessing organs through body orifices or smaller, puncture-like incisions. As a direct result thereof, patients tend to benefit from less scarring and reduced healing time.
Laparoscopic instruments are inserted into the patient through a cannula, or port, which has been made with a trocar. Typical sizes for cannulas range from three millimeters to twelve millimeters. Smaller cannulas are usually preferred, which, as can be appreciated, ultimately presents a design challenge to instrument manufacturers who must find ways to make laparoscopic instruments that fit through the smaller cannulas. Prior art RF vessel sealing devices require a table-top power-and-signal supply box connected to the electrodes of the jaws through a cumbersome power-and-signal supply line. The supply box takes up precious room within an operating suite. In addition, the supply box is expensive to produce, requiring the surgeon/hospital to expend significant amounts of capital to keep the unit on hand. Additionally, the supply line adds cost to produce and maintain. Importantly, the supply line commonly interferes with the surgeon's full freedom of movement during use.
Recently, the inventors have developed state of the art electrosurgical devices, such as RF bipolar vessel sealers and ultrasonic scalpel/vessel sealers, which allow all of the components to be contained in a single hand-held device, thus alleviating the heavy and expensive countertop box. This development is due, in part, to the creative use of small and light-weight but powerful battery packs that have, for example, transformed the hand-held commercial and consumer power tool markets over the past several years. This technology has already found its way into the operating room in the form of orthopedic drills, saws, and screwdrivers. However, batteries applied to cautery power supplies provide unique technical hurdles due to the limitations of their power-delivery characteristics.
For example, as current flows through a battery pack, its voltage drops due to its inherent internal impedance. This limits its capability to deliver maximum power. If the load to which the battery is connected differs in impedance greatly from its internal impedance, the battery cannot deliver its full power potential. This limitation cripples the ability of the battery pack to compete with a mains-powered box as a viable alternative.
Present lithium-ion battery packs are capable of delivering power in the 200 W range, which is ample power to perform a satisfactory vessel seal. However, due to an increase in the impedance of the tissue during desiccation, the battery cannot deliver this level of power throughout the entire sealing process. More specifically, the impedance of biologic tissue is in the 3-Ohm range. Desiccated tissue can develop an impedance as high as about 100 Ohms. Because the internal impedance of a typical Li-ion battery pack is only about 0.8 Ohms, a battery feeding a fixed-turns-ratio transformer cannot be made to accommodate the very wide impedance range and deliver power to its potential during an operation. If the impedance of the load could be made to more closely match the impedance of the battery, then the battery would be able to provide the necessary power.
Thus, a need exists to overcome the problematic issues discussed above.